1. Field of the Invention
The present invention relates to a method and apparatus for controlling power consumption in a display apparatus, particularly a display apparatus having a plasma display panel, and more particularly a display apparatus having an AC-driven plasma display panel. The invention also relates to a display system equipped with such a power consumption control apparatus, and a storage medium storing therein a program for implementing such a power consumption control method.
2. Description of the Related Art
Traditionally, power consumption control in a display apparatus, particularly a display apparatus having an AC-driven plasma display panel (PDP), has been performed by continuously monitoring power consumption that changes with changing display data, and by reducing the brightness of the entire screen when the power consumption exceeds its upper limit value and increasing the brightness when the power consumption drops below its lower limit value.
On the other hand, Japanese Unexamined Patent Publication No. 6-332397 discloses a control method in which display ratio is calculated by cumulatively adding display signals applied externally during a prescribed period, especially, one frame period, and the power consumption is controlled by setting the screen brightness to a value appropriate to the display ratio.
According to the former control method, when the display changes from ALL OFF to ALL ON state, since the screen brightness has been controlled up to the maximum during the ALL OFF period, the entire screen goes into the ALL ON state while the brightness is still controlled at the maximum value and, therefore, the power consumption at this time is higher than the predetermined value and the brightness must be reduced. If the speed with which the brightness is reduced is slow, the displayed image becomes gradually dark even when there is no change in the input display data. If the speed is increased, the image will appear to flash momentarily. In either case, an image quality problem will occur.
Such a problem does not occur with the latter control method since feedback control is not performed in the latter method. Not performing feedback control, however, involves a problem in that the power consumption relative to the display ratio varies from one display panel to another because of manufacturing variations.